1. Field of the Invention
The invention relates generally to stepper motors and more particularly to a digitally controllable electronic damper for providing pulses to a stepper motor whereby oscillations of the rotor of the stepper motor are damped.
2. Description of the Prior Art
Stepper motors are widely used for discrete positioning control and there are numerous applications for discrete positioning. A common application for stepper motors is the positioning of a part or work piece in which holes are to be drilled. The part is clamped to a table which is movable in an X and/or Y orthogonal direction. One stepper motor controls the movement of the table in the X direction and another stepper motor controls the movement of the table in the Y direction. A computer may be programed to provide control signals to control movement of the table, via the stepper motors, to a predetermined position and then drill a hole in the part. Control signals may then be generated and control movement of the table to another position where another hole is drilled. This procedure may be continued for as many holes as are necessary to be drilled in the part.
At the end of a stepping operation, the rotor of a stepper motor will oscillate for a period of time before coming to rest. This can become critical where positioning must be done at high speeds. For example, in high speed printers stepper motors are used to rotate rotor platen which feeds the paper through the printer. If the oscillations were to occur while the printer was typing a line, the print would come out uneven. Thus, it is desirable to dampen the oscillations before beginning to print. However, the time to accomplish such damping consumes time and the overall speed of the printer is decreased.
Damping may be accomplished by mechanical or electronic means. One form of electronic damping which is commonly used is known as delayed-last-step damping. This method utilizes the highly oscillatory nature of the rotor response to its advantage by delaying the last pulse to the stepper motor until such time as the torque provided is minimum. Delayed-last-step damping is described in the proceedings of the Second Annual Symposium on Incremental Motion Control Systems and Devices, 1973, pages H1 through H-13, and the proceedings of the Seventh Annual Symposium on Incremental Motion Control Systems and Devices, 1978, pages 283 through 289.
Delayed-last-step damping requires that the timing of pulses to the stepper motor be adjusted each time the number of steps to be moved is changed.